1. Field of the Invention
The present invention relates generally to a mechanism for connecting the seat and back of a chair to permit predetermined relative movement thereof and, more particularly, to a novel four bar linkage mechanism which provides for self-adjusting back tension of a chair as a user is seated therein.
2. Description of the Related Art
Seating articles, such as chairs, often include mechanisms to provide position adjustment of various parts of the chairs. This is particularly true of chairs used in office environments where office workers are frequently seated over long periods of time. These adjustments can include, for example, modification of the chair seat relative to floor level, modification of the chair back rest angle relative to an initial vertical position, and modification of chair seat angle relative to an initial horizontal position. All of these adjustments can contribute to the comfort of the chair user by selectively altering the user's body position when seated. Typically, these adjustments are accomplished by chair control mechanisms which include linkage systems of various types including spring biasing means.
One type of prior art chair control is illustrated in U.S. Pat. No. 2,272,980. This type of control permits the back of the chair to tilt while the chair seat is maintained in a fixed position. However, a drawback of this arrangement is that the seat is not at all adjustable. Further, the position of the chair back cannot be varied when the chair is in its task position.
Another form of chair control that has proved to be comfortable for the user is disclosed in early U.S. Pat. No. 2,083,838. This patent illustrates a body weight actuated chair wherein the back rest is adapted to be automatically adjusted to the back of the occupant when the occupant is positioned on the seat of the chair. This allows the user to recline somewhat in the chair while his or her feet remain placed on the floor. The weight of the user's body against the chair back acts through a slide mechanism to raise the seat back. While this construction allows for a degree of comfort to the user a disadvantage of the chair is that the slide mechanism is subject to wear and consequent binding over periods of use. Therefore, in practice it has a somewhat limited life and is lacking in reliability. Accordingly, it is desirable to provide a novel chair control mechanism which permits self-adjusting tension of the back of the chair. It is further desirable to provide such a mechanism which is operable solely in response to weight shift by the chair user on the seat of the chair. Still further, it is desirable to provide such a mechanism which is readily manufacturable and reliable in use.